1. Field of the Invention
The present invention relates to an image communicating apparatus, and more particularly to an image communicating apparatus capable of transmitting and/or receiving a color image.
2. Related Background Art
With the recent progress in the functions of the image recording means and image display means, the color copying machines and the color printers are becoming rapidly popular, and, also in the field of image communicating apparatus, color facsimile apparatus and similar products are being developed.
However such color copying machine or color facsimile apparatus is principally designed for the color image only, and is generally more bulky and more expensive than the apparatus for handling monochromatic image.
On the other hand, the communication method for the color facsimile is being standardized under the ITU-T recommendation (formerly CCITT recommendation), and the JPEG (Joint Photographic Expert Group) system, for color image encoding, is already adopted as a part of T.80 series.
Also as the recording method for the color facsimile, there are already known the thermal sublimation transfer method, thermal fusion transfer method, electrophotographic method, ink jet recording method etc., among which the former three are superior in the color reproducing capability and are suitable for use in the apparatus designed exclusively for the color image, but are expensive in the running cost. On the other hand, the ink jet recording method is already used in the color printers, and is attracting attention as an inexpensive method easily adaptable to color image and black-and-white image, though it is inferior in the color reproducing ability to the former three.
As explained in the foregoing, color image processing has become popular in the communication equipment, and various products have been commercialized in the field of color facsimile, but such products need to be improved in the following aspects:
1. high price and high running cost; PA1 2. inconvenient for black-and-white image handling, in the exclusive-color apparatus; PA1 3. difficulty in expansion of color function, from the current G3 facsimile format; and PA1 4. deterioration of characters, by JPEG process, in the header information of the transmitting side. PA1 1) The amount of information of a full-color image is 24 times of that of a black-and-white binary image of a same resolving power, so that a large cost is required for the image memory; PA1 2) The color recording unit by the thermal transfer method or the electrophotographic method requires a high manufacturing cost; PA1 3) The thermal transfer method or the electrophotographic method requires a special color recording sheet, leading to a high running cost; PA1 4) The ink jet recording method is less expensive in the cost of the recording unit and in the running cost, but requires frequent ink replenishment, because of the often limited ink capacity.
These aspects will be individually discussed in more details in the following:
1. High price and high running cost:
The color facsimile apparatus is at least 5 to 10 times more expensive than the ordinary G3 facsimile apparatus, and the running cost is also high, because of the following reasons:
2. Inconvenience for black-and-white image handling, in the exclusive-color apparatus:
If the running cost in the recording unit is high, the running cost for the black-and-white image becomes also high, so that the apparatus becomes usable only for the color image. Consequently the user wishing to handle the monochromatic images and the color images equally has to purchase the inexpensive monochromatic apparatus and the expensive color apparatus, so that the efficiency of office space becomes lower and the cost of purchase is also burdensome.
For this reason there is required an inexpensive color facsimile apparatus capable of monochromatic image handling equivalent to that in the ordinary monochromatic apparatus and also of transmission and reception of the color image.
Besides, the document to be transmitted is in most cases not composed of color pages only, but usually contains the color image and the monochromatic image in mixed manner in the unit of pages, for example a top page of monochromatic text followed by color pages. Transmission of such document entirely in the color mode will deteriorate the transmission speed, and the image quality of the monochromatic page is often deteriorated.
3. Difficulty of expansion of color function from the current G3 facsimile format:
The ability to communicate with the currently most popular G3 facsimile is an important feature, but the color function is not standardized in the G3 format but is realized only between the apparatus of a same manufacturer, according to a mode specific thereto. Thus the color image communication between the apparatus of different manufacturers is not possible by the protocol signals based on the current G3 standard.
4. Deterioration of characters by the JPEG process, in the header information of the transmitting side:
Most G3 facsimile apparatus adds, in the transmission, the header information as a part of the transmitted image. The header information generally includes the telephone number and abbreviation of the transmitting terminal, calendar information such as year, month, date and time, and the transmitted page number. Such header information is developed, at the transmitting side, from the character information into the image data, then subjected to binary compression encoding (such as MH encoding) and transmitted to the receiving side.
However, in the transmission of a multi-value color image by the JPEG process, it is already known, if such header information is added to the image and subjected to such JPEG process, that the characters contained in said header information are significantly deteriorated by the properties of JPEG process and often become illegible depending upon the character size. For this reason, in the color image transmission, it is required to use larger characters in the header information in order to maintain legibility. This leads to a drawback that the area of the header information becomes larger in the image reproduced at the receiving side.